Electric motor and reduction motor

ABSTRACT

Disclosed is a windshield wiper motor having a reduction mechanism unit and an electric motor. The electric motor of the windshield wiper motor includes a yoke formed in a bottomed cylindrical shape; permanent magnets arranged on an inner peripheral surface of the yoke; an armature including a rotary shaft journalled to the yoke, an armature core where a plurality of teeth are formed and fixed onto the rotary shaft, an armature coil wound around teeth of the armature core, a commutator having a plurality of segments and being fixed onto the rotary shaft, and a plurality of connecting wires connecting two segments arranged to face each other back to back around the rotary shaft, being surrounded by the permanent magnets and arranged within the yoke; and a first brush, a second brush, and a third brush coming into sliding contact with the segments of the commutator of the armature.

TECHNICAL FIELD

The present invention relates to an electric motor mounted on, forexample, a vehicle, and particularly, to a reduction motor.

This application is a continuation application based on a U.S. patentapplication Ser. No. 12/998,316, whose priority is claimed on JapanesePatent Application No. 2008-260987 filed on October 7 and incorporatingthe contents of this Japanese Patent Application by reference.

BACKGROUND ART

In the related art, electric motors with brushes have been used as wipermotors for an automobile. In this type of electric motor, a plurality ofpermanent magnets are arranged at equal intervals in the circumferentialdirection on the inner peripheral surface of a cylindrical yoke, and anarmature is surrounded by these permanent magnets and rotatablysupported by the yoke. The armature has an armature core, and aplurality of teeth is formed in a radial fashion on the armature core.Slots are spaces that are formed between the respective teeth. Electriccoils are wound so as to surround the plurality of teeth through twoslots. The armature has a rotary shaft, and a commutator is fixed to therotary shaft.

The commutator includes an insulating body formed in a columnar shape,and segments including a plurality of metal pieces. The plurality ofsegments are insulated from each other and disposed side by side alongthe circumferential direction on the insulating body. A winding startingend and a winding finishing end of an electric coil are connected toeach of these segments. A brush comes into sliding contact with eachsegment, and an electric current is supplied to each electric coil viathe segment from this brush. A magnetic field passing through thearmature core is generated by the electric current supplied to theelectric coil, and the armature is rotated together with the rotaryshaft by a magnetic attractive force or repulsive force that isgenerated between the permanent magnets fixed to the yoke and thearmature core.

In recent years, demands for miniaturization and high performance of thewiper motors are increasing. As a result, there is known a wiper motorthat includes magnets of which the number of magnetic poles is four (thenumber of pole pairs is two), an armature with more teeth, and fourbrushes and that enables changes in rotational speed (for example, referto Patent Document 1). In the motor disclosed in this Patent Document 1,patterns of energization to the four brushes are changed, and each modeof a low-speed rotation mode, a medium-speed rotation mode, and ahigh-speed rotation mode is selected. This motor includes the armaturewith four magnetic poles and a number of teeth, and the rotating speedof the armature is variable.

PRIOR ART DOCUMENT Patent Document

-   [Patent Document 1] Japanese Unexamined Patent Application, First    Publication No. 2006-353019

DISCLOSURE OF THE INVENTION Problem that the Invention is to Solve

Incidentally, in the above-described motor, gaps are respectivelypresent between the four permanent magnets disposed on an innerperipheral surface of the yoke. Thus, changes in magnetic flux betweenthe permanent magnet side and the gaps increase with both ends of eachpermanent magnet as boundarys. For this reason, when respective teeth ofthe armature passes by both the ends of each permanent magnet, amagnetic attractive force or repulsive force that acts between the teethand the magnet change greatly, and thereby cogging torque is generated.As a result, the vibration and noise of the electric motor increase.

The invention has been made in view of the above-describedcircumstances, and provides an electric motor and a reduction motor thatcan reduce vibration and noise while achieving miniaturization and highperformance, and that can also change the rotational speed of the motor.

Means for Solving the Problems

A first invention related to the invention is a windshield wiper motorhaving a reduction mechanism unit including an output shaft that drivesa wiper device of a vehicle; and an electric motor that drives thereduction mechanism. In this windshield wiper motor, the electric motorincludes a yoke formed in a bottomed cylindrical shape; four magnetsarranged in a cylindrical shape on an inner surface of the yoke so thatmagnetic poles thereof are arranged so as to be alternate with eachother; an armature including a rotary shaft rotatably supported by theyoke, an armature core fixed to the rotary shaft and including any teethof fourteen teeth, eighteen teeth, and twenty two teeth, a commutatorbeing fixed to the rotary shaft and including a plurality of segmentsinsulated from each other with the same number as the number of theteeth of the armature core, an armature coil being wound so as tosurround predetermined teeth of the armature core and including aplurality of winding wires having two terminals connected to theadjacent segments of the commutator, and a plurality of connecting wiresrespectively connected to the segments arranged to face each otheraround the rotary shaft, and being surrounded by the four magnets andaccommodated within the yoke; and a first brush, a second brush, and athird brush coming into sliding contact with the segments of thecommutator. In this windshield wiper motor, the first brush and thesecond brush are arranged apart in an angle of substantially 90 degreesfrom each other, the third brush is arranged apart in an angle of 90degrees or more from the first brush and the second brush, the firstbrush is connected to a common potential, an electric current forrotating the armature at low speed is selectively supplied to the secondbrush, an electric current for rotating the armature at high speed isselectively supplied to the third brush, and when the second brush comesinto sliding contact with a first segment of the commutator, the thirdbrush comes into sliding contact with an adjacent segment adjacent to afirst equipotential segment connected to the first segment by theconnecting wire, and does not come into sliding contact with the firstequipotential segment.

According to a second invention related to the invention, in the firstinvention, a width of the third brush is made smaller than a width ofthe first brush and a width of the second brush.

According to a third invention related to the invention, in the firstinvention, when the second brush comes into sliding contact with thefirst segment of the commutator and further a second segment adjacent tothe first segment, the third brush is arranged at a position that doesnot come into sliding contact with a first equipotential segmentconnected to the first segment of the commutator by a first connectingwire and a second equipotential segment connected to the second segmentby a second connecting wire.

According to a fourth invention related to the invention, in the firstinvention, when the second brush comes into sliding contact with thefirst segment of the commutator and further a second segment adjacent tothe first segment, the third brush is arranged at a position that comesinto sliding contact with a third equipotential segment connected to athird segment adjacent to the second segment of the commutator by athird connecting wire.

According to a fifth invention related to the invention, in the firstinvention, the armature coil of the armature includes a plurality offirst winding wires formed by a first conductive wire, and a pluralityof second winding wires formed by a second conductive wire, theplurality of first winding wires and the plurality of second windingwires are arranged point-symmetrically, and respective ends of theplurality of first winding wires and the plurality of second windingwires are connected to predetermined segments of the commutator.

According to a sixth invention related to the invention, in the fifthinvention, the connecting wires of the armature include a plurality offirst connecting wire portions formed by the first conductive wire and aplurality of second connecting wire portions formed by the secondconductive wire, and the plurality of first connecting wire portionsconnect the plurality of first winding wires in series, and theplurality of second connecting wire portions connect the plurality ofsecond winding wires in series.

According to a seventh invention related to the invention, in the fifthinvention, each of the plurality of first and second winding wires ofthe armature coil of the armature has a first semi-coil wound aroundfirst four teeth of a core body of the armature core, and a secondsemi-coil wound to surround second four teeth adjacent to the first fourteeth, and the winding direction of the first semi-coil and the windingdirection of the second semi-coil are opposite to each other.

According to an eighth invention related to the invention, in the firstinvention, the armature coil of the armature includes a plurality offirst winding wires formed by the first conductive wire and a pluralityof second winding wires formed by the second conductive wire, the firstwinding wires and the second winding wires are arrangedpoint-symmetrically, the connecting wires of the armature include aplurality of first connecting wire portions formed by the firstconductive wire and a plurality of second connecting wire portionsformed by the second conductive wire, the plurality of first connectingwire portions connect the plurality of first winding wires in series,and the plurality of second connecting wire portions connect theplurality of second winding wires in series, each of the plurality offirst and second winding wires of the armature coil of the armature hasa first semi-coil wound around first four teeth of a core body of thearmature core and a second semi-coil wound to surround second four teethadjacent to the first four teeth, and the winding direction of the firstsemi-coil and the winding direction of the second semi-coil are oppositeto each other.

A ninth invention related to the invention is a windshield wiper motorhaving a reduction mechanism unit including an output shaft that drivesa wiper device of a vehicle; and an electric motor that drives thereduction mechanism. In this windshield wiper motor, the electric motorincludes a yoke formed in a bottomed cylindrical shape; four magnetsarranged in a cylindrical shape on an inner surface of the yoke so thatmagnetic poles thereof are arranged so as to be alternate with eachother; an armature including a rotary shaft rotatably supported by theyoke, an armature core fixed to the rotary shaft and including eighteenteeth, a commutator being fixed to the rotary shaft and including aplurality of segments insulated from each other with the same number asthe number of the teeth of the armature core, an armature coil beingwound so as to surround predetermined teeth of the armature core andincluding a plurality of winding wires having two terminals connected tothe adjacent segments of the commutator, and eighteen connecting wiresrespectively connected to the segments arranged to face each otheraround the rotary shaft, and being surrounded by the four magnets andaccommodated within the yoke; and a first brush, a second brush, and athird brush coming into sliding contact with the segments of thecommutator. In this windshield wiper motor, the first brush and thesecond brush are arranged apart by an angle of substantially 90 degreesfrom each other, the third brush is arranged apart by an angle of 90degrees or more from the first brush and the second brush, the firstbrush is connected to a common potential, an electric current forrotating the armature at low speed is selectively supplied to the secondbrush, an electric current for rotating the armature at high speed isselectively supplied to the third brush, a width of the third brush ismade smaller than a width of the first brush and a width of the secondbrush and when the second brush comes into sliding contact with thefirst segment of the commutator, the third brush comes into slidingcontact with an adjacent segment adjacent to a first equipotentialsegment connected to the first segment by the connecting wire, and doesnot come into sliding contact with the first equipotential segment.

According to a tenth invention related to the invention, in the ninthinvention, when the second brush comes into sliding contact with thefirst segment of the commutator and further a second segment adjacent tothe first segment, the third brush is arranged at a position that doesnot come into sliding contact with a first equipotential segmentconnected to the first segment of the commutator by a first connectingwire and a second equipotential segment connected to the second segmentby a second connecting wire.

According to an eleventh invention related to the invention, in theninth invention, when the second brush comes into sliding contact withthe first segment of the commutator and further a second segmentadjacent to the first segment, the third brush is arranged at a positionthat comes into sliding contact with a third equipotential segmentconnected to a third segment adjacent to the second segment of thecommutator by a third connecting wire.

According to a twelfth invention related to the invention, in the ninthinvention, the armature coil of the armature includes a plurality offirst winding wires formed by a first conductive wire, and a pluralityof second winding wires formed by a second conductive wire, theplurality of first winding wires and the plurality of second windingwires are arranged point-symmetrically, and respective ends of theplurality of first winding wires and the plurality of second windingwires are connected to predetermined segments of the commutator.

According to a thirteenth invention related to the invention, in thetwelfth invention, the connecting wires of the armature include aplurality of first connecting wire portions formed by the firstconductive wire and a plurality of second connecting wire portionsformed by the second conductive wire, and the plurality of firstconnecting wire portions connect the plurality of first winding wires inseries, and the plurality of second connecting wire portions connect theplurality of second winding wires in series.

According to a fourteenth invention related to the invention, in thetwelfth invention, each of the plurality of first and second windingwires of the armature coil of the armature has a first semi-coil woundaround first four teeth of a core body of the armature core, and asecond semi-coil wound to surround second four teeth adjacent to thefirst four teeth, and the winding direction of the first semi-coil andthe winding direction of the second semi-coil are opposite to eachother.

According to a fifteenth invention related to the invention, in theninth invention, the armature coil of the armature includes a pluralityof first winding wires formed by the first conductive wire and aplurality of second winding wires formed by the second conductive wire,the first winding wires and the second winding wires are arrangedpoint-symmetrically, the connecting wires of the armature include aplurality of first connecting wire portions formed by the firstconductive wire and a plurality of second connecting wire portionsformed by the second conductive wire, the plurality of first connectingwire portions connect the plurality of first winding wires in series,and the plurality of second connecting wire portions connect theplurality of second winding wires in series, each of the plurality offirst and second winding wires of the armature coil of the armature hasa first semi-coil wound around first four teeth of a core body of thearmature core and a second semi-coil wound to surround second four teethadjacent to the first four teeth, and the winding direction of the firstsemi-coil and the winding direction of the second semi-coil are oppositeto each other.

Advantageous Effects of Invention

In the invention, since the plurality of teeth of the armature core areformed on the core body at equal intervals along the circumferentialdirection, the respective teeth and the respective slots are presentpoint-symmetrically around the rotary shaft. On the other hand, a slotis present at a position apart by an angle of 90 degrees from a tooth inthe circumferential direction of the armature core. As a matter ofcourse, a tooth is present at a position apart by an angle of 90 degreesfrom a slot in the circumferential direction of the armature core. Forthis reason, when a tooth passes through one end of each permanentmagnet, a slot passes through the other end. Therefore, changes in amagnetic attractive force or repulsive force that acts between the teethand the magnet do not occur simultaneously at both ends of eachpermanent magnet, and the changes in the magnetic attractive force orrepulsive force occur so as to shift from each other by ½ pitch of thepitch between two slots of the armature. Accordingly, the cogging torquedecreases on average. As a result, the vibration and noise of theelectric motor decrease.

That is, the vibration and noise are reduced by selecting any of 7times, 9 times, and 11 times the number of pole pairs (two) as thenumber of teeth and slots. For this reason, a high-performance electricmotor and a reduction motor can be provided.

The circumferential width of the high-speed brush is set to be smallerthan the circumferential width of the low-speed brush, and a situationwhere the high-speed brush simultaneously comes into sliding contactwith a segment having the same potential as a segment that comes intosliding contact with the low-speed brush is avoided.

Here, in a case where the electric motor is rotatably driven at lowspeed, as the high-speed brush that is not used comes into slidingcontact with two segments, a coil connected to the two segments isshort-circuited, the number of effective coils decreases, and variationoccurs in electric currents that flow through respective coils. As aresult, the vibration and noise of the electric motor may increase.

However, influence of the high-speed brush during low rotational drivingcan be made small by setting the circumferential width of the high-speedbrush to be smaller than the circumferential width of the low-speedbrush. For this reason, an electric motor and a reduction motor withless vibration and noise can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a reduction motor according to an embodiment ofthe invention.

FIG. 2 is a longitudinal cross-sectional view of the reduction motoraccording to the embodiment of the invention.

FIG. 3 is a cross-sectional view of an electric motor according to theembodiment of the invention.

FIG. 4 is a view as seen from arrow A of FIG. 2.

FIG. 5 is a development view of an armature according to the embodimentof the invention.

MODES FOR CARRYING OUT THE INVENTION

Next, an embodiment of the invention will be described with reference tothe drawings.

As shown in FIGS. 1 to 3, a reduction motor 1 is used as, for example, awiper motor of an automobile, and includes an electric motor 2, and areduction mechanism 4 connected to a rotary shaft 3 of the electricmotor 2.

The electric motor 2 has a bottomed cylindrical yoke 5, and an armature6 rotatably provided within the yoke 5.

A tubular portion 53 of the yoke 5 is formed in a substantiallycylindrical shape, and four segment type permanent magnets 7 aredisposed at equal intervals in a circumferential direction on the innerperipheral surface of the tubular portion 53 such that magnetic polesare alternate. That is, the permanent magnets 7 provided at the yoke 5generate a magnetic field with two pole pairs.

The center of a bottom wall (an end portion) 51 of the yoke 5 is formedwith a boss portion 19 that protrudes outward, and a bearing 18 forjournalling one end of the rotary shaft 3 is fixed to the boss portion19.

An opening 53 a of the tubular portion 53 is provided with an outerflange portion 52. The outer flange portion 52 is formed with abolt-hole (not shown). A bolt 24 is inserted through this bolt-hole, andthe yoke 5 is fixed to the reduction mechanism 4 as the bolt 24 isscrewed into a bolt-hole (not shown) formed in a gear housing 23 of thereduction mechanism 4.

The armature 6 includes the rotary shaft 3, an armature core 8 fixed tothe rotary shaft 3, an armature coil 9 wound around the armature core 8,and a commutator 10 fixed onto the rotary shaft 3. The armature core 8has a core body 11 formed from a laminated core formed by laminatingplates made of a magnetic material punched by press working or the likeor a dust core formed by pressure-forming soft magnetic powder.

At an outer peripheral portion of the core body 11, eighteen teeth 12,which are substantially T-shaped, are provided in a radial fashion atequal intervals along the circumferential direction at the outerperipheral portion. Each tooth 12 is constituted by a winding drumportion 31 that extends in a radial direction and has a winding wire 14wound therearound, and a peripheral wall portion 32 that is provided atthe tip of the winding drum portion 31 and extends so as to bebilaterally symmetrical with respect to the winding drum portion 31.That is, the peripheral wall portion 32 provided at the tip of the tooth12 constitutes the outer peripheral surface of the armature core 8, andthe peripheral wall portion 32 faces a permanent magnet 7.

Eighteen groove-shaped slots 13 are formed between eighteen teeth 12 byproviding the teeth 12 in a radial fashion at the outer peripheralportion of the core body 11. The slots 13 extend along the axialdirection of the rotary shaft 3, and are formed at equal intervals alongthe circumferential direction.

The winding wire 14 coated with enamel is inserted through the slots 13,and the winding wire 14 is wound around the teeth 12. As a result, thearmature coil 9 is formed on the armature core 8.

As the eighteen teeth 12 are formed on the core body 11 at equalintervals along the circumferential direction, the respective teeth 12and the respective slots 13 are present point-symmetrically around therotary shaft 3, respectively. On the other hand, the teeth 12 and theslots 13 are alternately present in a positional relationship withintervals of 90 degrees in the circumferential direction.

The permanent magnets 7 have four generated magnetic poles and two polepairs, whereas eighteen teeth 12 and eighteen slots 13 are provided.That is, the number of the teeth 12 is set to 9 times the number of polepairs.

Additionally, the respective teeth 12 and the respective slots 13 arepoint-symmetrical around the rotary shaft 3, and the teeth 12 and theslots 13 are present alternately at positions apart by an angle of 90degrees from each other in the circumferential direction of the armaturecore 8. Thus, each tooth 12 that faces an N-pole permanent magnet 7 andeach teeth 12 that faces an S-pole permanent magnet 7 shift from eachother by a ½ pitch.

Eighteen segments 15 formed from a conductive material are attached ontothe outer peripheral surface of the commutator 10. The segments 15 aremade of a plate-like metal piece that is long in the axial direction,and are fixed onto the outer peripheral surface of the commutator 10 inparallel at equal intervals along the circumferential direction in astate where the segments are insulated from each other. The externaldiameter D1 of the commutator 10 is set within a range of 20 mm or moreand 30 mm or less.

A riser 16 is molded at the end of each segment 15 near the armaturecore 8. The winding wire 14 that becomes a winding starting end and awinding finishing end of the armature coil 9 is connected to the riser16 by fusing or the like. As a result, a segment 15 and the armaturecoil 9 corresponding to this segment are electrically connected to eachother.

Additionally, a connecting wire 40 is connected to the risers 16 of twoequipotential segments 15, that is, the risers 16 of two segments 15(the risers 16 of every pair of segments 15 separated by nine positionsin the present embodiment) that face each other around the rotary shaft3 or the risers 16 of two segments 15 apart by an angle of 180 degreesfrom each other by fusing or the like (refer to FIG. 5). The connectingwire 40 is provided to short-circuit the equipotential segments 15 fromeach other, and is disposed between the commutator 10 and the armaturecore 8. A connecting wire portion is formed at the connecting wire 40 ina place where the connecting wires 40 and the commutator 10 areconnected.

The commutator 10 configured in this way is arranged within the gearhousing 23 of the reduction mechanism 4. The gear housing 23 isconstituted by a housing body 42 that is formed in a substantially boxshape, and a cover 43 that blocks an opening 42 a of the housing body42. A gear group 41 of the reduction mechanism 4 is housed in thehousing body 42. Additionally, a brush housing portion 22 is formed atthe housing body 42, and brushes 21 together with the commutator 10 ofthe electric motor 2 are accommodated in the housing body.

A peripheral wall 30 of the brush housing portion 22 is formed so as tohave a substantially oval cross-section, and is constituted by planarwalls 30 a and circular-arc walls 30 b.

A cover 33, which is formed in the shape of a tube having asubstantially oval cross-section so as to correspond to the brushhousing portion, is provided inside the brush housing portion 22. Thecover 33 also has planar walls 33 a and circular-arc walls 33 b.Moreover, a holder stay 34 formed so as to correspond to the cover 33 isprovided inside the cover 33. The holder stay 34 is fastened and fixedto a side wall 42 b of the housing body 42 by bolts 35.

Brush holders 36 are provided in three places along the circumferentialdirection at the holder stay 34. The brushes 21 are biased by springs S,respectively, and accommodated within the brush holders 36,respectively. Since the brushes 21 are biased by the springs S, the tipportions of the brushes 21 come into sliding contact with the segments15 of the commutator 10, and the electric current from an external powersource (not shown) is supplied to the commutator 10 via the brushes 21.

The brushes 21 are constituted by a low-speed brush 21 a and ahigh-speed brush 21 b, which are connected to an anode of the externalpower source, and a common brush 21 c that is used common to thelow-speed brush 21 a and the high-speed brush 21 b and is connected to acathode of the external power source. The low-speed brush 21 a and thecommon brush 21 c are arranged apart at an electrical angle of 180° fromeach other, that is, apart at a mechanical angle of 90 degrees in thecircumferential direction of the commutator 10 from each other.Meanwhile, the high-speed brush 21 b is arranged apart by an angle α inthe circumferential direction from the low-speed brush 21 a. Inaddition, although the present embodiment has been described that thecommon brush 21 c is connected to the cathode of the external powersource, and the low-speed brush 21 a and the high-speed brush 21 b areconnected to the anode of the external power source, the anode andcathode may be connected in a reversed manner. Additionally, adescription will be provided with a first brush, a second brush, and athird brush in the invention as the common brush 21 c, the low-speedbrush 21 a, and the high-speed brush 21 b, respectively.

In addition, the electric resistance value of the high-speed brush 21 bis set to be two or more times higher than the electric resistancevalues of the low-speed brush 21 a and the common brush 21 c. Therefore,the current value of an electric current supplied from the high-speedbrush 21 b to the armature coil 9 is lowered. For example, when anelectric current is supplied from the high-speed brush 21 b to thearmature coil 9 and the armature 6 of the electric motor 2 is rotatingat high speed, the current value of a lock current supplied to thearmature coil 9 is prevented from increasing in a case where therotation of the armature 6 is stopped (locked) by an external load.Therefore, any unnecessary damage to an element for protecting anelectric circuit, such as a fuse provided in a motor drive device, isprevented in advance.

In addition, as for two equipotental segments 15 connected by aconnecting wire 40, if a brush 21 comes into sliding contact with onesegment 15, an electric current is also supplied via the connecting wire40 to the other segment 15 with which the brush 21 does not come intosliding contact. The high-speed brush 21 b is arranged at a positionthat is advanced by an angle θ from the low-speed brush 21 a. Inaddition, in the present embodiment, the angle θ is set to about 30degrees.

By arranging the low-speed brush 21 a, the high-speed brush 21 b, andthe common brush 21 c in this way, the shapes of the cover 33 and theholder stay 34 become reasonable shapes. That is, the cover 33 is formedso as to have a substantially oval cross-section, and the low-speedbrush 21 a and the common brush 21 c are arranged at connecting portionsbetween the planar walls 33 a and the circular-arc wall 33 b. On theother hand, the high-speed brush 21 b is arranged at the circular-arcwall 33 b of the cover 33 opposite to places, where the low-speed brush21 a and the common brush 21 c are arranged, around the rotary shaft 3.For this reason, the brush housing portion 22 is formed so as to have asubstantially oval cross-section, and it is accordingly possible to formthe brush housing portion 22 in a flattend shape.

Additionally, as shown in detail in FIG. 3, the brush widths W1 in thecircumferential direction in which the low-speed brush 21 a and thecommon brush 21 c come into sliding contact with the commutator 10 areset to be almost the same. In contrast, the brush width W2 in thecircumferential direction in which the high-speed brush 21 b comes intosliding contact with the commutator 10 is set to be smaller than thebrush width W1 of the low-speed brush 21 a. Specifically, when theexternal diameter of the commutator 10 is set within a range of 20 mm ormore and 30 mm or less, the brush widths W1 of the low-speed brush 21 aand the common brush 21 c are set within a range of 2.5 mm or more and 5mm or less. On the other hand, the brush width W2 of the high-speedbrush 21 b is set to be in a range that is equal to and more than 1.5 mmand smaller than 2.5 mm.

By appropriately setting the brush widths W1 of the low-speed brush 21 aand the common brush 21 c and the brush width W2 of the high-speed brush21 b in this way, and by appropriately arranging the low-speed brush 21a, the common brush 21 c, and the high-speed brush 21 b with respect toeach other, it is possible to avoid a situation where the low-speedbrush 21 a and the high-speed brush 21 b simultaneously come intosliding contact with segments 15 having the same potential as eachother. Hereinafter, a detailed description thereof will be provided.

Since two segments 15 apart by an angle of 180 degrees from each otherare connected by a connecting wire 40 connected to the commutator 10,for example, a segment 15 that comes into sliding contact with thelow-speed brush 21 a, and a segment 15 apart by 180 degrees from thissegment have the same potential. Accordingly, as the commutator 10, avirtual low-speed brush 21 a is like being present even at a positionshown by a two-dotted chain line in FIG. 3, and an electric current issupplied to the segment 15 that is apart by 180 degrees. In this case,the spacing between the virtual low-speed brush 21 a and the high-speedbrush 21 b becomes almost the same as the width of the segments 15 asshown in FIG. 3. However, since the brush width W2 of the high-speedbrush 21 b is set to be smaller than the brush width W1 of the low-speedbrush 21 a, it is possible to avoid a situation where the low-speedbrush 21 a and the high-speed brush 21 b simultaneously come intosliding contact with segments 15 having the same potential as eachother.

This is also the same in the high-speed brush 21 b and the common brush21 c. On the other hand, a high-speed brush 21 b is considered to bepresent even at a position point-symmetrical around the rotary shaft 3by a connecting wire 40 connected to the commutator 10. However, sincethe brush width W2 of the high-speed brush 21 b is set to be smallerthan the brush width W1 of the common brush 21 c, a situation where avirtual high-speed brush 21 b and the common brush 21 c simultaneouslycome into sliding contact with the same segments 15 is avoided.

As shown in FIGS. 1 and 2, the gear group 41 housed in the housing body42 of the gear housing 23 is constituted by a worm shaft 25 coupled tothe rotary shaft 3 of the electric motor 2, a stepped gear 26 thatmeshes with the worm shaft 25, and a spur gear 27 that meshes with thestepped gear 26. The worm shaft 25 has one end coupled to the rotaryshaft 3 and the other end rotatably journalled on the housing body 42.The stepped gear 26 is obtained by integrally forming a worm wheel 28that meshes with the worm shaft 25, and a smaller-diameter gear 29 thatis formed to have a smaller diameter than the worm wheel 28.

An idler shaft 61 is press-fitted into the radial center of the steppedgear 26. The idler shaft 61 protrudes to the side opposite to thesmaller-diameter gear 29, and the protruding end 61 a is rotatablyjournalled on the housing body 42. On the other hand, the tip of thesmaller-diameter gear 29 that is present at the end of the idler shaft61 opposite to the end 61 a is rotatably journalled on the cover 43. Inthis way, the stepped gear 26 is brought into a state where both endsthereof are journalled to the housing body 42 and the cover 43.

The spur gear 27 meshes with the smaller-diameter gear 29 of the steppedgear 26. A boss portion 65 is formed at the radial center of the spurgear 27 so as to protrude toward the cover 43 side. The boss portion 65is rotatably supported by the cover 43. Additionally, an output shaft 62is press-fitted into the boss portion 65. The output shaft 62 protrudesfrom a bottom wall (an end portion) 42 c of the housing body 42. A bossportion 63 is formed at the part of the bottom wall 42 c of the housingbody 42 corresponding to the output shaft 62 so as to protrude outward.The boss portion 63 is provided with a sliding bearing 64 for rotatablyjournalling the output shaft 62.

The portion of the output shaft 62 that protrudes from the housing body42 is formed with a tapered portion 66 that is gradually tapered as itgoes to the tip. The tapered portion 66 is formed with serrations 67. Anexternal mechanism for driving a wiper or the like is coupled to theoutput shaft 62.

In addition, a connector 68 is provided at the side wall 42 b of thehousing body 42 so as to protrude along the axial direction of therotary shaft 3. The connector 68 is provided to supply the electricpower from the outside to the electric motor 2. A receiving port 69 ofthe connector 68 is provided with a connecting terminal 70, and theconnecting terminal 70 is electrically connected to the brushes 21 (21 ato 21 c) of the electric motor 2. Thereby, the electric power from theoutside is supplied to the commutator 10 via the brushes 21.

Moreover, bolt seats 71 for fastening and fixing the cover 43 are formedintegrally with an opening edge of the housing body 42. Attachment seats73, which has bolt-holes (not shown) through which bolts 72 can beinserted, are integrally formed at the parts of the cover 43corresponding to the bolt seats 71 of the housing body 42. In the cover43, as the bolts 72 are inserted through the attachment seats 73, andthe bolts 72 are screwed into the bolt seats 71 of the housing body 42,the cover 43 is fastened and fixed to the housing body 42.

Additionally, the cover 43 is provided with a power distributionsubstrate 74 for electrically connecting the connecting terminal 70 ofthe connector 68 and the brushes 21 of the electric motor 2. The powerdistribution substrate 74 is formed with a wiring pattern (not shown)that has the role of a lead wire.

Next, the structure for winding the winding wire 14 around the armaturecore 8 of the armature 6 will be described with reference to FIG. 5.

FIG. 5 is a development view of the armature 6, and gaps between twoadjacent teeth 12 correspond to the slots 13. In addition, in thefollowing drawings, the respective segments 15 and the respective teeth12 will be described with respective reference numerals given thereto.

As shown in detail in this drawing, two equipotential segments 15 areshort-circuited by a connecting wire 40. That is, in the presentembodiment, every pair of segments 15 (for example, a first segment 15and a tenth segment 15) separated by nine positions are short-circuitedby a connecting wire 40.

Here, the winding wire 14 is constituted by a first conductive wire 110and a second conductive wire 120. In addition, in FIG. 5, the firstconductive wire 110 is shown by solid lines, and the second conductivewire 120 is shown by broken lines.

A first coil 161 constituted by the first conductive wire 110 isconnected to a segment 15 (No. 12) of the commutator 10, is wound so asto surround a first tooth, a second tooth, a third tooth, and a fourthtooth of the teeth 12, passes through a slot 13 between the fourth toothand a fifth tooth of the teeth 12. Next, the first coil is wound in thebackward direction so as to surround the fifth tooth, a sixth tooth, aseventh tooth, and an eighth tooth of the teeth 12, and is connected toa segment 15 (No. 11) of the commutator 10.

A first coil 171 constituted by the second conductive wire 120 isconnected to a segment 15 (No. 3) of the commutator 10, is wound so asto surround a tenth tooth, an eleventh tooth, a twelfth tooth, and athirteenth tooth of the teeth 12, passes through a slot 13 between thethirteenth tooth and a fourteenth tooth of the teeth 12. Next, thesecond coil is wound in the backward direction so as to surround thefourteenth tooth, a fifteenth tooth, a sixteenth tooth, and aseventeenth tooth of the teeth 12, and is connected to a segment 15 (No.2) of the commutator 10.

The first conductive wire 110 connected to the segment 15 (No. 11) ofthe commutator 10 becomes a connecting wire 40, and is connected fromthe segment (No. 11) of the commutator 10 to the segment (No. 2). Thefirst conductive wire 110 becomes a coil 162 from the segment (No. 2),is wound so as to surround a ninth tooth, the tenth tooth, the eleventhtooth, and the twelfth tooth of the teeth 12, passes through a slot 13between the twelfth tooth and the thirteenth tooth of the teeth 12.Next, the first conductive wire is wound in the backward direction so asto surround the thirteenth tooth, the fourteenth tooth, the fifteenthtooth, and the sixteenth tooth of the teeth 12, and is connected to asegment (No. 1) of the commutator 10.

Similarly, a coil 163, a coil 164, a coil 165, a coil 166, a coil 167, acoil 168, and a coil 169 are wound. The coil 163 is connected to asegment (No. 10) and a segment (No. 9), the coil 164 is connected to asegment (No. 18) and a segment (No. 17), the coil 165 is connected to asegment (No. 8) and a segment (No. 7), the coil 166 is connected to asegment (No. 16) and a segment (No. 15), the coil 167 is connected to asegment (No. 6) and a segment (No. 5), the coil 168 is connected to asegment (No. 14) and a segment (No. 13), and the coil 169 is connectedto a segment (No. 4) and a segment (No. 3).

The connecting wires 40 are also formed by the first conductive wire 110between the segment (No. 9) and the segment (No. 18), between thesegment (No. 7) and the segment (No. 16), between the segment (No. 15)and the segment (No. 6), and between the segment (No. 13) and thesegment (No. 4).

The second conductive wire 120 connected to the segment (No. 2) of thecommutator 10 becomes a connecting wire 40, and is connected from thesegment (No. 2) of the commutator 10 to the segment (No. 11). The secondconductive wire 120 becomes a coil 172 from the segment (No. 11), iswound so as to surround the eighteenth tooth, the first tooth, thesecond tooth, and the third tooth of the teeth 12, passes through a slot13 between the third tooth and the fourth tooth of the teeth 12. Next,the second conductive wire is wound in the backward direction so as tosurround the fourth tooth, the fifth tooth, the sixth tooth, and theseventh tooth of the teeth 12, is connected to the segment (No. 10) ofthe commutator 10.

Similarly, a coil 173, a coil 174, a coil 175, a coil 176, a coil 177, acoil 178, and a coil 179 are wound. The coil 173 is connected to thesegment (No. 1) and the segment (No. 18), the coil 174 is connected tothe segment (No. 9) and the segment (No. 8), the coil 175 is connectedto the segment (No. 17) and the segment (No. 16), the coil 176 isconnected to the segment (No. 7) and the segment (No. 6), the coil 177is connected to the segment (No. 15) and the segment (No. 14), the coil178 is connected to the segment (No. 5) and the segment (No. 4), and thecoil 179 is connected to the segment (No. 13) and the segment (No. 12).

The connecting wires 40 are also formed by the first conductive wire 110between the segment (No. 18) and the segments (No. 9), between thesegment (No. 16) and the segment (No. 7), between the segment (No. 6)and segment (No. 15), and between the segment (No. 4) and the segment(No. 13).

As shown in FIG. 5, when the low-speed brush 21 a is connected to thesegment (No. 2) and the segment (No. 3), the high-speed brush 21 b isnot connected to the segment (No. 11) and the segment (No. 12) that areconnected to the segment (No. 2) and the segment (No. 3) by theconnecting wire 40, and the high-speed brush 21 b is connected to thesegment (No. 13) adjacent to the segment (No. 12). The first to ninthwinding wires 161 to 169 formed by the first conductive wire 110 and thefirst to ninth winding wires 171 to 179 formed by the second conductivewire 120 are arranged at positions that are respectivelypoint-symmetrical around the rotary shaft 3. The first conductive wire110 includes a first semi-coil wound around four teeth and a secondsemi-coil wound around four teeth, and the first semi-coil and thesecond semi-coil are wound in the opposite direction. This is also thesame in the second conductive wire 120.

That is, the first winding wire 161 formed by the first conductive wire110 and the other first winding wire 171 formed by the second conductivewire 120 are present at positions that face each other around the rotaryshaft 3, and a first winding wire pair is formed by the winding wire 161and the winding wire 171. Similarly, a second winding wire pair (162,172), a third winding wire pair (163, 173), a fourth winding wire pair(164, 174), a fifth winding wire pair (165, 175), a sixth winding wirepair (166, 176), a seventh winding wire pair (167, 177), an eighthwinding wire pair (168, 178), and a ninth winding wire pair (169, 179)are formed by the second to ninth winding wires 162 to 169 and the othersecond to ninth winding wires 172 to 179, respectively.

The first to ninth winding wires 161 to 169 are connected in a seriesvia nine connecting wires 40, respectively. On the other hand, the otherfirst to ninth winding wires 171 to 179 are connected in a series vianine connecting wires 40, respectively. A winding starting end and awinding finishing end of each of the winding wires 161 to 179 areconnected between adjacent segments 15 and 15. The winding wires 161 to169 and the winding wires 171 to 179 are wound using, for example, adouble flyer type winding machine or the like.

Next, the operation of the reduction motor 1 will be described.

First, during low rotational driving, electric power is supplied to theelectric motor 2 of the reduction motor 1 through the common brush 21 cand the low-speed brush 21 a. At this time, a magnetic field isgenerated by an electric current flowing through the armature coil 9wound around the armature core 8, and magnetic attractive or repulsiveforces are generated between this magnetic field and magnetic fieldsgenerated by the permanent magnets 7 provided at the yoke 5 to drive therotary shaft 3 of the armature 6. On the other hand, during highrotational driving, electric power is supplied to the high-speed brush21 b, and the electric motor 2 operates at a higher rotational speedthan that during the low rotational driving.

When the rotary shaft 3 rotates, the rotative force of the rotary shaft3 is transmitted to the output shaft 62 via the reduction mechanism 4.Since an external mechanism for driving a wiper or the like is coupledto the output shaft 62, the external mechanism operates at low speed oroperates at high speed as the output shaft 62 rotates.

Here, the respective teeth 12 and the respective slots 13 of theelectric motor 2 are arranged point-symmetrically around the rotaryshaft 3. Since the teeth 12 are eighteen, a slot 13 is present at aposition apart by an angle of 90 degrees from one tooth 12 and a tooth12 is present at a position apart by an angle of 90 degrees from oneslot 13. Since four permanent magnets 7 are arranged at equal intervals,teeth 12 that face two ends of each permanent magnet 7 a are shiftedfrom each other by ½ pitch.

For this reason, cogging torques generated in the armature 6 at the endsof each magnet 7 are generated so as to shift from each other by ½ ofthe pitch of the interval between the teeth 12. That is, the samecogging torque is not generated simultaneously at both ends of themagnet 7. As a result, the cogging torque is reduced. Hence, the coggingtorque of the whole electric motor 2 decreases.

During the low rotational driving, electric power is supplied to thearmature 6 through the common brush 21 c and the low-speed brush 21 a,electric power is not supplied to the high-speed brush 21 b. For thisreason, when the high-speed brush 21 b simultaneously contacts twoadjacent segments 15 and 15, the segments 15 and 15 are short-circuitedby the high-speed brush 21 b. Electric currents supplied through thecommon brush 21 c and the low-speed brush 21 a do not flow to thewinding wire 14 connected to the two short-circuited segments 15 and 15.

At this time, since magnetic flux generated by the magnet 7 passesthrough the winding wire 14 that becomes a closed loop by the high-speedbrush 21 b, an induced voltage (counter-electromotive force) isgenerated in the winding wire 14 due to a change in this magnetic flux,and electric current flows to the winding wire 14. The direction of thiselectric current is opposite to the direction of the electric currentssupplied from the common brush 21 c and the low-speed brush 21 a, and ifa large electric current continues flowing, a torque ripple increases.

However, in the present embodiment, the brush widths W1 of the low-speedbrush 21 a and the common brush 21 c in the circumferential directionare set to be almost the same as each other, and the circumferentialbrush width W2 of the high-speed brush 21 b is set to be smaller thanthe brush width W1 of the low-speed brush 21 a (refer to FIG. 3). Forthis reason, the time for which the high-speed brush 21 b contacts twoadjacent segments 15 and 15 becomes short. Additionally, since theresistance value of the high-speed brush 21 b increases, an electriccurrent that flows into the winding wire 14 in which a closed loop isformed by the high-speed brush 21 b decreases.

On the other hand, since electric power is supplied to the armature 6through the common brush 21 c and the high-speed brush 21 b during thehigh rotational driving, electric power is not supplied to the low-speedbrush 21 a. In a case where the low-speed brush 21 a contacts twoadjacent segments 15 and 15, the winding wire 14 connected to the twosegments 15 and 15 are also short-circuited. However, an induced voltage(counter-electromotive force) is scarcely generated in theshort-circuited winding wire 14. This is because the low-speed brush 21a is arranged at a position where an induced voltage(counter-electromotive force) is scarcely generated in the winding wire14, and contacts the two adjacent segments 15 and 15 at that position.

Therefore, according to the above-described embodiment, there isprovided the armature 6 in which the number of pole pairs is two, thatis, the number of magnetic poles is four, and the numbers of teeth 12are 7 times (fourteen), 9 times (eighteen), and 11 times (twenty two)the number of pole pairs. Thus, the cogging torque can be reduced evenin the variable-speed electric motor 2. For this reason, the vibrationand noise of the electric motor 2 (reduction motor 1) are reduced.

Particularly, an increase in the torque ripple resulting from thehigh-speed brush 21 b can be reduced during the low rotational drivingwith high use frequency compared to the high rotational driving. Forthis reason, it is possible to further reduce the vibration and noise ofthe electric motor 2 during the low rotational driving.

Additionally, by setting the circumferential brush width W2 of thehigh-speed brush 21 b to be smaller than the circumferential brushwidths W1 of the low-speed brush 21 a and the common brush 21 c, asituation where the low-speed brush 21 a and the high-speed brush 21 bsimultaneously come into sliding contact with the same segments 15 isavoided.

In addition, it should be understood that the invention is not limitedto the above-described embodiment, and various modifications may be madeto the above-described embodiment without departing from the spirit ofthe invention.

Additionally, a case where the armature core 8 of the electric motor 2is provided with eighteen teeth 12, and the number of the teeth 12 isset to 9 times the number of pole pairs has been described in theabove-described embodiment. However, the number of teeth 12 is notlimited to this and the number of teeth 12 may be set to any of 7 times,9 times, and 11 times the number of pole pairs.

INDUSTRIAL APPLICABILITY

As described above, according to the invention, it is possible toprovide a variable-speed electric motor and a reduction motor that canreduce vibration and noise while achieving miniaturization and highperformance.

REFERENCE SIGNS LIST

-   -   1: REDUCTION MOTOR    -   2: ELECTRIC MOTOR    -   3: ROTARY SHAFT    -   4: REDUCTION MECHANISM    -   5: YOKE    -   6: ARMATURE    -   7: PERMANENT MAGNET (MAGNETIC POLE)    -   8: ARMATURE CORE    -   9: ARMATURE COIL (COIL)    -   10: COMMUTATOR    -   12: TEETH    -   13: SLOT    -   14: WINDING WIRE (COIL)    -   15: SEGMENT    -   21: BRUSH    -   21 a: LOW-SPEED BRUSH    -   21 b: HIGH-SPEED BRUSH    -   21 c: COMMON BRUSH    -   25: WORM SHAFT    -   28: WORM WHEEL    -   40: CONNECTING WIRE (SHORT-CIRCUITING MEMBER)    -   D1: EXTERNAL DIAMETER    -   W1, W2: BRUSH WIDTH

The invention claimed is:
 1. A windshield wiper motor comprising: areduction mechanism unit including an output shaft that drives a wiperdevice of a vehicle; and an electric motor that drives the reductionmechanism, wherein the electric motor comprising: a yoke formed in abottomed cylindrical shape; four magnets arranged in a cylindrical shapeon an inner surface of the yoke so that magnetic poles thereof arearranged so as to be alternate with each other; an armature including arotary shaft rotatably supported by the yoke, an armature core fixed tothe rotary shaft and including any teeth of fourteen teeth, eighteenteeth, and twenty two teeth, a commutator being fixed to the rotaryshaft and including a plurality of segments insulated from each otherwith the same number as the number of the teeth of the armature core, anarmature coil being wound so as to surround predetermined teeth of thearmature core and including a plurality of winding wires having twoterminals connected to the adjacent segments of the commutator, and aplurality of connecting wires respectively connected to the segmentsarranged to face each other around the rotary shaft, and beingsurrounded by the four magnets and accommodated within the yoke; and afirst brush, a second brush, and a third brush coming into slidingcontact with the segments of the commutator, wherein the first brush andthe second brush are arranged apart by an angle of substantially 90degrees from each other, wherein the third brush is arranged apart by anangle of 90 degrees or more from the first brush and the second brush,wherein the first brush is connected to a common potential, wherein anelectric current for rotating the armature at low speed is selectivelysupplied to the second brush, wherein an electric current for rotatingthe armature at high speed is selectively supplied to the third brush,and wherein when the second brush comes into sliding contact with afirst segment of the commutator, the third brush comes into slidingcontact with an adjacent segment adjacent to a first equipotentialsegment connected to the first segment by the connecting wire, and doesnot come into sliding contact with the first equipotential segment. 2.The windshield wiper motor according to claim 1, wherein a width of thethird brush is made smaller than a width of the first brush and a widthof the second brush.
 3. The windshield wiper motor according to claim 1,wherein when the second brush comes into sliding contact with the firstsegment of the commutator and further a second segment adjacent to thefirst segment, the third brush is arranged at a position that does notcome into sliding contact with a first equipotential segment connectedto the first segment of the commutator by a first connecting wire and asecond equipotential segment connected to the second segment by a secondconnecting wire.
 4. The windshield wiper motor according to claim 1,wherein when the second brush comes into sliding contact with the firstsegment of the commutator and further a second segment adjacent to thefirst segment, the third brush is arranged at a position that comes intosliding contact with a third equipotential segment connected to a thirdsegment adjacent to the second segment of the commutator by a thirdconnecting wire.
 5. The windshield wiper motor according to claim 1,wherein the armature coil of the armature includes a plurality of firstwinding wires formed by a first conductive wire, and a plurality ofsecond winding wires formed by a second conductive wire, wherein theplurality of first winding wires and the plurality of second windingwires are arranged point-symmetrically, and wherein respective ends ofthe plurality of first winding wires and the plurality of second windingwires are connected to predetermined segments of the commutator.
 6. Thewindshield wiper motor according to claim 5, wherein the connectingwires of the armature include a plurality of first connecting wireportions formed by the first conductive wire and a plurality of secondconnecting wire portions formed by the second conductive wire, andwherein the plurality of first connecting wire portions connect theplurality of first winding wires in series, and the plurality of secondconnecting wire portions connect the plurality of second winding wiresin series.
 7. The windshield wiper motor according to claim 5, whereineach of the plurality of first and second winding wires of the armaturecoil of the armature has a first semi-coil wound around first four teethof a core body of the armature core, and a second semi-coil wound tosurround second four teeth adjacent to the first four teeth, and whereinthe winding direction of the first semi-coil and the winding directionof the second semi-coil are opposite to each other.
 8. The windshieldwiper motor according to claim 1, wherein the armature coil of thearmature includes a plurality of first winding wires formed by the firstconductive wire and a plurality of second winding wires formed by thesecond conductive wire, wherein the first winding wires and the secondwinding wires are arranged point-symmetrically, wherein the connectingwires of the armature include a plurality of first connecting wireportions formed by the first conductive wire and a plurality of secondconnecting wire portions formed by the second conductive wire, whereinthe plurality of first connecting wire portions connect the plurality offirst winding wires in series, and the plurality of second connectingwire portions connect the plurality of second winding wires in series,wherein each of the plurality of first and second winding wires of thearmature coil of the armature has a first semi-coil wound around firstfour teeth of a core body of the armature core and a second semi-coilwound to surround second four teeth adjacent to the first four teeth,and wherein the winding direction of the first semi-coil and the windingdirection of the second semi-coil are opposite to each other.
 9. Awindshield wiper motor comprising: a reduction mechanism unit includingan output shaft that drives a wiper device of a vehicle; and an electricmotor that drives the reduction mechanism, wherein the electric motorcomprising: a yoke formed in a bottomed cylindrical shape; four magnetsarranged in a cylindrical shape on an inner surface of the yoke so thatmagnetic poles thereof are arranged so as to be alternate with eachother; an armature including a rotary shaft rotatably supported by theyoke, an armature core fixed to the rotary shaft and including eighteenteeth, a commutator being fixed to the rotary shaft and including aplurality of segments insulated from each other with the same number asthe number of the teeth of the armature core, an armature coil beingwound so as to surround predetermined teeth of the armature core andincluding a plurality of winding wires having two terminals connected tothe adjacent segments of the commutator, and eighteen connecting wiresrespectively connected to the segments arranged to face each otheraround the rotary shaft, and being surrounded by the four magnets andaccommodated within the yoke; and a first brush, a second brush, and athird brush coming into sliding contact with the segments of thecommutator, wherein the first brush and the second brush are arrangedapart by an angle of substantially 90 degrees from each other, whereinthe third brush is arranged apart by an angle of 90 degrees or more fromthe first brush and the second brush, wherein the first brush isconnected to a common potential, wherein an electric current forrotating the armature at low speed is selectively supplied to the secondbrush, wherein an electric current for rotating the armature at highspeed is selectively supplied to the third brush, wherein the width ofthe third brush is made smaller than the width of the first brush andthe width of the second brush, and wherein when the second brush comesinto sliding contact with a first segment of the commutator, the thirdbrush comes into sliding contact with an adjacent segment adjacent to afirst equipotential segment connected to the first segment by theconnecting wire, and does not come into sliding contact with the firstequipotential segment.
 10. The windshield wiper motor according to claim9, wherein when the second brush comes into sliding contact with thefirst segment of the commutator and further a second segment adjacent tothe first segment, the third brush is arranged at a position that doesnot come into sliding contact with a first equipotential segmentconnected to the first segment of the commutator by a first connectingwire and a second equipotential segment connected to the second segmentby a second connecting wire.
 11. The windshield wiper motor according toclaim 9, wherein when the second brush comes into sliding contact withthe first segment of the commutator and further a second segmentadjacent to the first segment, the third brush is arranged at a positionthat comes into sliding contact with a third equipotential segmentconnected to a third segment adjacent to the second segment of thecommutator by a third connecting wire.
 12. The windshield wiper motoraccording to claim 9, wherein the armature coil of the armature includesa plurality of first winding wires formed by a first conductive wire,and a plurality of second winding wires formed by a second conductivewire, wherein the plurality of first winding wires and the plurality ofsecond winding wires are arranged point-symmetrically, and whereinrespective ends of the plurality of first winding wires and theplurality of second winding wires are connected to predeterminedsegments of the commutator.
 13. The windshield wiper motor according toclaim 12, wherein the connecting wires of the armature include aplurality of first connecting wire portions formed by the firstconductive wire and a plurality of second connecting wire portionsformed by the second conductive wire, and wherein the plurality of firstconnecting wire portions connect the plurality of first winding wires inseries, and the plurality of second connecting wire portions connect theplurality of second winding wires in series.
 14. The windshield wipermotor according to claim 12, wherein each of the plurality of first andsecond winding wires of the armature coil of the armature has a firstsemi-coil wound around first four teeth of a core body of the armaturecore, and a second semi-coil wound to surround second four teethadjacent to the first four teeth, and wherein the winding direction ofthe first semi-coil and the winding direction of the second semi-coilare opposite to each other.
 15. The windshield wiper motor according toclaim 9, wherein the armature coil of the armature includes a pluralityof first winding wires formed by the first conductive wire and aplurality of second winding wires formed by the second conductive wire,wherein the first winding wires and the second winding wires arearranged point-symmetrically, wherein the connecting wires of thearmature include a plurality of first connecting wire portions formed bythe first conductive wire and a plurality of second connecting wireportions formed by the second conductive wire, wherein the plurality offirst connecting wire portions connect the plurality of first windingwires in series, and the plurality of second connecting wire portionsconnect the plurality of second winding wires in series, wherein each ofthe plurality of first and second winding wires of the armature coil ofthe armature has a first semi-coil wound around first four teeth of acore body of the armature core and a second semi-coil wound to surroundsecond four teeth adjacent to the first four teeth, and wherein thewinding direction of the first semi-coil and the winding direction ofthe second semi-coil are opposite to each other.